1. Field of the Invention
The present invention relates to an electrical safety apparatus which is capable of detecting leakage current from an electric appliance and blocking the current from being applied to an electric appliance, and in particular, but not exclusively, to an improved leakage current alarming/blocking apparatus which is capable of effectively preventing an electric shock by detecting a leakage current of an electric appliance such as a washing machine, refrigerator, microwave oven, motor, electric heater, etc. using an antiphase transformer in which the AC (Alternating Current) of a secondary side of a transformer is antiphased based on a ground potential, blocking electric power from being applied to the electric appliance to prevent an electric shock to a user.
2. Description of the Conventional Art
Generally, an electric appliance such as washing machine, refrigerator, microwave oven, motor, electric heater, etc. is housed with a conductive material such as a steel plate. Therefore, if a leakage current is applied to the surface of the above-described electric appliance, a user may experience an electric shock when in contact with the exposed portion of the electric appliance.
In order to overcome the above-described problems, there are a few known methods. First, the surfaces of the product are coated with a non-conductive material (for example, paint). The non-conductive material provides insulation between the user and the surface of the appliance. If there is any leakage current in the surface, the user will not become part of the circuit and experience an electric shock. Second, a ground terminal is installed and then connected with a ground potential (or a ground terminal having a ground potential) through a ground cable. The ground cable is connected to the ground potential. If there is any leakage current present in the surface of the appliance, it will flow to the ground potential. The user avoids an electric shock by not becoming the ground terminal. Third, the electric appliance is supplied with an electric power through a circuit breaker. The circuit breaker blocks any leakage current.
However, among the above-described electric shock prevention methods, there are some problems. Namely, in the first method, when the coated non-conductive material is exposed due to scratch, abrasion, impact, etc., the user may come into contact with the exposed portion and receive an electric shock. In addition, in the second method, the conductive material of the product may not be connected with the ground potential due to an installation error by a user or simply by an accidental disconnection. For example, a ground cable is extended from the product at a predetermined length and is connected with the ground potential. If the installation site of the product is far from the ground potential, it is impossible to connect the ground cable with the ground potential, and the connection is never made.
Microwave ovens or refrigerators are generally installed in the kitchen, and washing machines are installed in places where there are few taps. The above-described places are remote from ground, so that it becomes virtually impossible to ground electric appliances. In addition, in some buildings, the ground port of a three-port wall outlet is not grounded. Therefore, the ground line extended from the ground terminal of the electric appliance is not grounded.
The third method for applying electric power to the electric appliance through the circuit breaker also has problems. When a human body contacts with an electric appliance which is electrically exposed, a closed loop of "Electric power supplying terminal.fwdarw.Conductive material of electric appliance.fwdarw.Human body.fwdarw.Ground" is formed. When current flowing in the human body exceeds a heart beating rate of 50 mA per second, the human body is electrically shocked. Therefore, the circuit breaker is generally designed to have an electric shock current of below 30 mA and an operation time of below 0.1 seconds. However, when applying an electric power using the abovedescribed circuit breaker, the following problems may occur. First, it is impossible to detect the leakage current when the electric appliance is not grounded. Second, since the electric appliance is grounded using the ground terminal and line, if the electric line connected with the electric appliance is cut or electric power supplied to the electric appliance is turned on or off, it would become impossible to detect the leakage current.
In the conventional circuit breaker for the leakage current, the amount of the current applied through the circuit breaker and the amount of the current fed back through the closed loop are detected. If it is determined that the two current values are different, it is concluded that there is leakage current. If there is a situation where the electric lines to the appliance are cut, no leakage current will flow and therefore not be detected. So even if there is leakage current, it will not be detected therefore exposing a user to a potential shock.